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Schmallenberg Virus: Analysis of Epidemiological Data

24 November 2012

The analysis intends to give an overview of the disease in all affected countries one year after outbreak.

Following the request from the European Commission for EFSA to continue to collect data and provide updates of the epidemiological situation of Schmallenberg virus (SBV) in the EU. This epidemiological report presents the analysis of the data received during the reporting period, updating the previously published report on the analysis of the epidemiological data and preliminary assessment of impact.

The analysis intends to give an overview of the SBV situation after 1 year (reporting period from 1 August 2011 till 31 July 2012) together with an update of newly affected herds.

All affected countries have reported the number of confirmed herds following viral detection by PCR, virus neutralisation test or serological confirmation. An increased number of test results is based on serological detection of SBV antibodies and this can only be used as evidence of infection but provide no information on clinical disease or occurrence of new cases. No new cases were reported from Spain or Belgium.

In August 2012, 294 herds were reported with AHS symptoms in cattle. In September and October the number of herds with AHS symptoms decreased however acute cases in adults (adult animals where clinical signs were observed and SBV diagnosis confirmed) were reported in August, September and October .

It is important to note that the number of countries reporting acute adult cases is limited and it is likely that adult cases are not diagnosed considering the transitory and non specific nature of the clinical signs observed. An increase of the number of AHS cases is likely to occur in the coming months resulting of infection of previously unexposed animals in the susceptible period of gestation.

The temporal analysis was performed for SBV confirmed herd reports. It can be seen that the SBV has continued to circulate within Europe with newly affected herds being reported in October 2012.

At the time of publication of the last EFSA epidemiological update in May 8 member states (Belgium, France, Germany, Italy, Luxembourg, the Netherlands, Spain and United Kingdom) had reported confirmed cases of SBV. During the summer SBV confirmed cases were reported in new countries; including Denmark, Finland, Poland, Sweden and Switzerland, and in new regions in France, United Kingdom and Germany.

Other epidemiology reporting services indicate that SBV has also been detected in Austria and Ireland. SBV is continuing to spread to new areas of Europe, and it is likely that new SBV cases will be observed in Southern and Eastern regions of Europe in 2013.

The data available only allows a between herd impact assessment based upon the comparison between SBV confirmed herds and the total number of herds in each affected region by species. For all affected countries, the number of SBV confirmed herds is low compared with the total number of herds.

The maximum proportion of confirmed sheep herds per region is 6.6 pper cent and 4 per cent for cattle herds. Nevertheless, these comparisons should be interpreted cautiously since under reporting or lack of confirmation may affect the ratio. No information is available to assess within herd impact.